hasdata

Return true if there is more data in datastore

Since R2020a

Syntax

tf = hasdata(sds)

Description

tf = hasdata(sds) returns logical 1 (true) if there is data available to read from the datastore specified by sds. Otherwise, it returns logical 0 (false).

Examples

Read File Data in Signal Datastore

Specify the path to a set of audio signals included as MAT-files with MATLAB®.

folder = fullfile(matlabroot,"toolbox","matlab","audiovideo");

Create a signal datastore that points to the specified folder and set sample rate variable name to Fs. List the names of the MAT-files in the datastore.

sds = signalDatastore(folder, ...
    FileExtension=".mat",SampleRateVariableName="Fs");
[~,c] = fileparts(sds.Files)

c = 7x1 cell
    {'chirp'   }
    {'gong'    }
    {'handel'  }
    {'laughter'}
    {'mtlb'    }
    {'splat'   }
    {'train'   }

While the signal datastore has unread files, read consecutive files from the datastore. Use the progress function to monitor the fraction of files read.

while hasdata(sds)
    [data,info] = read(sds);
    fprintf("Fraction of files read: %.2f\n",progress(sds))
end

Fraction of files read: 0.14
Fraction of files read: 0.29
Fraction of files read: 0.43
Fraction of files read: 0.57
Fraction of files read: 0.71
Fraction of files read: 0.86
Fraction of files read: 1.00

Print and inspect the info structure returned by the last call to the read function.

info

info = struct with fields:
             SampleRate: 8192
       TimeVariableName: "Fs"
    SignalVariableNames: "y"
               FileName: "/mathworks/devel/bat/filer/batfs2566-0/Bdoc24b.2725827/build/runnable/matlab/toolbox/matlab/audiovideo/train.mat"

Find Spectrogram of Chirps

The sample_chirps folder contains sample files included with Signal Processing Toolbox™. Each file contains a chirp and a random sample rate, fs, ranging from 100 to 150 Hz. Create a signal datastore that points to four of the files in sample_chirps and specify the name of the sample rate variable.

addpath("sample_chirps")
files = ["chirp_1.mat","chirp_4.mat","chirp_9.mat","chirp_10.mat"];
sds = signalDatastore(files,SampleRateVariableName="fs");

Define a function that takes the output of the read function and computes and returns:

• The spectrograms of the chirps.

• The vector of time instants corresponding to the centers of the windowed segments.

• The frequencies corresponding to the estimates.

function [dataOut,infoOut] = extractSpectrogram(dataIn,info)
    [dataOut,F,T] = pspectrum(dataIn,info.SampleRate,"spectrogram",...
                              TimeResolution=0.25,...
                              OverlapPercent=40,Leakage=0.8);
    infoOut = info;
    infoOut.CenterFrequencies = F;
    infoOut.TimeInstants = T;
end

Call the transform function to create a datastore that computes the spectrogram of each chirp using the function you defined.

sdsNew = transform(sds,@extractSpectrogram,IncludeInfo=true);

While the transformed datastore has unread files, read from the new datastore and visualize the spectrograms in three-dimensional space.

t = tiledlayout("flow");
while hasdata(sdsNew)
    nexttile
    [sig,infoOut] = read(sdsNew);
    waterfall(infoOut.TimeInstants,infoOut.CenterFrequencies,sig)
    xlabel("Frequency (Hz)")
    ylabel("Time (S)")
    view([30 70])
end

Compute Envelopes of Signals

Specify the path to four signals included with MATLAB®. The signals are recordings of a bird chirp, a gong, a train, and a splat. All signals are sampled at 8192 Hz.

folder = fullfile(matlabroot,'toolbox','matlab','audiovideo', ...
         ["chirp.mat","gong.mat","train.mat","splat.mat"]);

Create a signal datastore that points to the specified files. Each file contains the variable Fs that denotes the sample rate.

sds1 = signalDatastore(folder,'SampleRateVariableName','Fs');

Define a function that takes the output of the read function and calculates the upper and lower envelopes of the signals using spline interpolation over local maxima separated by at least 80 samples. The function also returns the sample times for each signal.

function [dataOut,infoOut] = signalEnvelope(dataIn,info)
    [dataOut(:,1),dataOut(:,2)] = envelope(dataIn,80,'peak');
    infoOut = info;
    infoOut.TimeInstants = (0:length(dataOut)-1)/info.SampleRate;
end

Call the transform function to create a second datastore, sds2, that computes the envelopes of the signals using the function you defined.

sds2 = transform(sds1,@signalEnvelope,"IncludeInfo",true);

Combine sds1 and sds2 create a third datastore. Each call to the read function from the combined datastore returns a matrix with three columns:

• The first column corresponds to the original signal.

• The second and third columns correspond to the upper and lower envelopes, respectively.

sdsCombined = combine(sds1,sds2);

Read and display the original data and the upper and lower envelopes from the combined datastore. Use the extractBetween function to extract the file name from the file path.

tiledlayout('flow')
while hasdata(sdsCombined)
    [dataOut,infoOut] = read(sdsCombined);
    ts = infoOut{2}.TimeInstants;
    nexttile
    hold on
    plot(ts,dataOut(:,1),'Color','#DCDCDC','LineStyle',':')
    plot(ts,dataOut(:,2:3),'Linewidth',1.5)
    hold off
    xlabel('Time (s)')
    ylabel('Signal')
    title(extractBetween(infoOut{:,2}.FileName,'audiovideo\','.mat'))
end

Input Arguments

sds — Signal datastore

signalDatastore object

Specify sds as an signalDatastore object.

Output Arguments

tf — Indication if data is available to read

true | false

Indication if data is available to read from the datastore, returned as true or false.

Data Types: logical

Version History

Introduced in R2020a